The molecular basis of the variation within and between species remains largely unknown. Standard genetic analyses in model organisms have focused on laboratory-induced mutations with large phenotypic effects. This type of qualitative and discrete variation contrasts with the variation seen in natural populations, which is mostly continuous. The genetic basis of the latter can be found in Quantitative Trait Loci (QTL), each of which contributes only a portion to the entire variation. The phenotypic variation seen within or between closely related species also contrasts with the phenotypic variation seen between more distantly related species. However, that intra- and interspecific variations are two sides of the same coin, although a unifying molecular framework has not been developed. A better understanding of this framework is being resolved with new technologies such as high-throughput genotyping, new statistical and computational methods, comprehensive transcriptome and proteome profiling, as well as opportunities to compare entire genomes between closely and distantly related organisms. Understanding the molecular basis of natural variation has important implications both for understanding the evolution of new traits, as well as for understanding how selection has shaped genomes, including the human genome. This is a very important topic, as it is only poorly understood why apparently detrimental alleles persist in the human population, where they contribute to many diseases with a strong genetic component. [unreadable] [unreadable] The meeting will focus both on animal and plant model organisms, in which the use of quantitative genetics is experiencing a renaissance. The molecular study of QTL, which have been traced back to individual genes, is allowing conclusions as to the type of genes and changes that underlie quantitative phenotypic variation. A second focus will be recent discoveries of how changes in key regulatory factors cause major phenotypic differences in more distantly related taxa. [unreadable] [unreadable]